The speed/quality can be adjusted using only 4 parameters:

1. noise threshold in DMC
2. global subdivs mult
3. subdivs at LC (in new VrayC4D it`s can be auto adjusted too)
4. resolution
The rest is not necessarily touch. Auto changes. This applies to all settings Ir map and DMC GI.

And yet! Use DMC AA 1/4. No Fixed!

(c) Saluto